Complete the recursive formula of the arithmetic sequence $-5, -25, -45, -65,...$. $b(1)=$
Answer: The first term is $-5$ and the common difference is $-20$. ${-20\,\curvearrowright}$ ${-20\,\curvearrowright}$ ${-20\,\curvearrowright}$ $-5,$ $-25,$ $-45,$ $-65,...$ This is the recursive formula of $-5, -25, -45, -65,...$ $\begin{cases} b(1)=-5 \\\\ b(n)=b(n-1)+(-20) \end{cases}$